Displacement detection device for variable displacement compressor

ABSTRACT

A displacement detection device for a variable displacement compressor in which a swash plate which is connected to a piston through shoes in a housing slides relative to the shoes and rotates synchronously with a drive shaft with a wobbling motion in an axial direction of the drive shaft as the drive shaft is rotated, and an inclination angle of the swash plate is controlled thereby changing a stroke of the piston, includes a detection object provided in a first portion of an outer periphery of the swash plate where an imaginary plane passing through a point of intersection between a line connecting top and bottom dead center positions of the swash plate and an axial line of the drive shaft in perpendicular relation to the line intersects with the outer periphery of the swash plate and a detector provided in the housing so as to face the detection object.

BACKGROUND OF THE INVENTION

The present invention relates to a displacement detection device in avariable displacement compressor for use in a vehicle air-conditioner.

There is generally known a variable displacement compressor (hereinafterreferred to merely as “compressor”) which is adapted for use in avehicle air-conditioner and operable to control its displacement. Such acompressor has a swash plate which is accommodated in a crank chamberand inclinable relative to a drive shaft of the compressor. As thepressure in the crank chamber is raised, the swash plate is inclinedtoward its vertical position with respect to the axis of the drive shaft(or the inclination angle of the swash plate is decreased). As thepressure in the crank chamber is lowered, on the other hand, the swashplate is inclined approaching the axis of the drive shaft or moving awayfrom its vertical position (or the inclination angle of the swash plateis increased). The compressor has a piston whose stroke length ischanged according to the inclination of the swash plate. When thepressure in the crank chamber is high and the inclination angle of theswash plate is small, the piston reciprocates for a short distance ofstroke thereby to provide a small displacement of the compressor. On theother hand, when the pressure in the crank chamber is low and theinclination angle of the swash plate is large, the piston reciprocatesfor a long distance of stroke thereby to provide a large displacement ofthe compressor.

Japanese Patent Application Publication No. 62-218670 discloses a wobbleplate type compressor (cf. Pages 2-5 and FIG. 1 of the publication).This compressor has a drive shaft rotatably supported in a crankchamber, a rotation support member mounted on the drive shaft and awobble plate fitting member coupled to the rotation support member. Thewobble plate fitting member is mounted on the drive shaft through ahinge ball. As the drive shaft is rotated, the wobble plate fittingmember is rotated while making a wobbling motion in the axial directionof the drive shaft. A wobble plate is supported by the wobble platefitting member through a bearing so that the wobble plate is rotatablerelative to the wobble plate fitting member. Pistons in cylinders whichare formed around the drive shaft in a cylinder block are connected tothe wobble plate through piston rods for reciprocating movement in therespective cylinders. Thus, the rotation of the drive shaft is convertedthrough the wobble plate fitting member into the reciprocating andwobbling motion of the wobble plate in the axial direction, therebycausing the piston to reciprocate in the cylinder for the compressor toperform suction and compression of refrigerant gas.

A pin or a magnet as an object to be detected projects from the outerperiphery of the wobble plate at a predetermined location. Anelectromagnetic induction type detector is disposed on the outerperipheral surface of the housing. The detector is located at a positionwhere the pin moves past the detector as the wobble plate wobbles and atthe center position of the wobbling motion path of the pin when thewobble plate is at its minimum inclination angle so that the detectingportion of the detector is located in facing relation to the pin. Thedetector is operable to detect the change of magnetic flux each time thepin passes the detecting portion and to also generate pulse signal,accordingly. The pulse signal is transmitted to a control unit which isconnected to the detector. According to the inputted pulse signal, thecontrol unit determines the periods of time during which the pin islocated on the left and right sides of the detecting portion of thedetector, respectively. It has been known that the ratio of eachdetermined period of time to the sum of both detected periods of time onthe left and right sides, namely to one complete cycle of the wobblingmotion, depends on the displacement of the compressor. By using this,the control unit calculates the inclination of the wobble plate andhence the displacement of the compressor.

In a swash plate type compressor in which the piston is connectedthrough shoes to the swash plate which has a sliding portion slidablerelative to the shoes and rotatable synchronously with a drive shaft,however, a pulse signal is generated per one rotation of the driveshaft. Thus, the structure disclosed in Japanese Patent ApplicationPublication No. 62-218670 cannot be used in such a swash plate typecompressor. In order to detect the displacement of the swash plate typecompressor, an object to be detected may be provided at an appropriateposition on the outer periphery of the swash plate and one or more ofdetectors may be provided in the compressor housing. The position of theswash plate is sensed by detecting the magnitude of magnetic flux whichvaries according to the distance between the detector and the detectionobject.

If the detection object is located at the top or bottom dead centerposition of the swash plate, the distance between the detection objectand the detector varies not only in the axial direction but also in theradial direction from the axis of the drive shaft as the inclinationangle of the swash plate is changed. Thus, for permitting the detectionin a wide range from the minimum inclination angle position of the swashplate to its maximum position, the detection output from the detector orthe magnetic force of the detection object need be increased. Inaddition, the above-described prior art compressor has a problem in thatthere is a need to correct the distance of the detection outputaccording to the inclination angle of the swash plate.

The present invention which has been made in view of the above-describedproblems is directed to a variable displacement compressor which iscapable of accurately detecting the angle of a swash plate.

SUMMARY OF THE INVENTION

An aspect in accordance with the present invention provides adisplacement detection device for a variable displacement compressor inwhich a swash plate is connected to a piston through shoes in a housing,the swash plate slides relative to the shoes and rotates synchronouslywith a drive shaft with a wobbling motion in an axial direction of thedrive shaft as the drive shaft is rotated, and an inclination angle ofthe swash plate is controlled thereby to change a stroke of the piston.The displacement detection device includes a detection object which isprovided in a first portion of an outer periphery of the swash platewhere an imaginary plane passing through a point of intersection betweena line connecting a top dead center position and a bottom dead centerposition of the swash plate and an axial line of the drive shaft inperpendicular relation to the line intersects with the outer peripheryof the swash plate and a detector which is provided in the housing so asto face the detection object.

Other aspects and advantages of the invention will become apparent fromthe following description, taken in conjunction with the accompanyingdrawings, illustrating by way of example the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel areset forth with particularity in the appended claims. The inventiontogether with objects and advantages thereof, may best be understood byreference to the following description of the presently preferredembodiments together with the accompanying drawings in which:

FIG. 1 is a longitudinal cross-sectional view of a variable displacementcompressor according to a first preferred embodiment of the presentinvention;

FIG. 2 is a cross-sectional view of taken along the line I-I in FIG. 1;

FIG. 3 is a schematic view explaining the detection of the inclinationangle of a swash plate according to the first preferred embodiment;

FIG. 4 is a schematic view as seen in the direction of the arrow B inFIG. 3;

FIG. 5 is a schematic view explaining the detection of the inclinationangle of a swash plate according to a second preferred embodiment;

FIG. 6 is a schematic view as seen in the direction of the arrow C inFIG. 5;

FIG. 7 is a cross-sectional view of a variable displacement compressoraccording to an alternative embodiment of the present invention;

FIG. 8 is a cross-sectional view of a variable displacement compressoraccording to an alternative embodiment of the present invention; and

FIG. 9 is a cross-sectional view of a variable displacement compressoraccording to an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe a variable displacement compressor(hereinafter referred to merely as “compressor”) according to a firstpreferred embodiment of the present invention with reference to FIGS. 1through 4. Referring to FIG. 1, the compressor 10 has a housing 11 as anouter shell which includes a cylinder block 12 defining therein aplurality of cylinder bores 12 a, a front housing 13 and a rear housing14. The front housing 13 is joined to the front end of the cylinderblock 12 and the rear housing 14 is joined to the rear end of thecylinder block 12. The front housing 13, the cylinder block 12 and therear housing 14 are integrally fastened to each other by a plurality ofbolts 15 (only one being shown in FIG. 1) inserted through the fronthousing 13, the cylinder block 12 and the rear housing 14.

The front housing 13 and the cylinder block 12 cooperate to define acrank chamber 16 through which a drive shaft 17 extends. The drive shaft17 is rotatably supported by a radial bearing 18 provided at the frontof the front housing 13 and a radial bearing 19 provided at the centerof the cylinder block 12. A shaft seal mechanism 20 is provided on thedrive shaft 17 at a position forward of the radial bearing 18 in slidecontact with the outer circumferential surface of the drive shaft 17.The drive shaft 17 is connected at its front end to an external drivesource (not shown) through a power transmission mechanism (not shown).

A lug plate 21 is secured to the drive shaft 17 in the crank chamber 16for rotation therewith. A swash plate 22 as a part of thedisplacement-changing mechanism of the compressor is provided behind thelug plate 21 and supported by the drive shaft 17 so as to be slidable inthe axial direction of the drive shaft 17 and also inclinable relativeto the axis of the drive shaft 17. A hinge mechanism 23 is interposedbetween the swash plate 22 and the lug plate 21 so that the swash plate22 and the lug plate 21 are connected therethrough. The hinge mechanism23 allows the swash plate 22 to rotate synchronously with and beinclined relative to the drive shaft 17 and the lug plate 21.

A coil spring 24 is disposed on the drive shaft 17 between the lug plate21 and the swash plate 22. A tubular body 25 is slidably disposed on thedrive shaft 17 and urged rearward by the coil spring 24. The tubularbody 25 urges the swash plate 22 rearward or in the direction whichcauses the inclination angle of the swash plate 22 to be decreased. Itis noted that the inclination angle of the swash plate 22 refers to anangle made between an imaginary plane perpendicular to the axis of thedrive shaft 17 and a flat surface of the swash plate 22.

The swash plate 22 has a stop 22 a projecting from the front thereof fordetermining the maximum inclination of the swash plate 22 by contactwith the lug plate 21 as shown in FIG 1. A retaining ring 26 is fittedon the drive shaft 17 rearward of the swash plate 22 and a coil spring27 is disposed on the drive shaft 17 between the retaining ring 26 andthe swash plate 22. The minimum inclination of the swash plate 22 isdetermined by the contact thereof with the front of the coil spring 27.In FIG. 1, the swash plate 22 indicated by the solid line is positionedat its maximum inclination angle and the swash plate 22 indicated by thetwo-dotted line is inclined at its minimum inclination angle.

Referring to FIG. 2, a magnet 35 as a detection object is provided inthe outer periphery of the swash plate 22 and a magnetic sensor 36 as adetector is provided in the peripheral wall 12 b of the cylinder block12 which faces the magnet 35. These elements will be described in detaillater.

Referring back to FIG. 1, a single-headed piston 28 is reciprocatablydisposed in each of the cylinder bores 12 a of the cylinder block 12(five cylinder bores in this preferred embodiment). The piston 28 isengaged at its neck with the outer periphery of the swash plate 22through a pair of shoes 29 in a manner well known in the art. The swashplate 22 has a sliding portion which is slidable relative to the shoes29 and rotatable synchronously with the drive shaft 17. As the driveshaft 17 is rotated, the swash plate 22 is rotated therewith whilemaking a wobbling motion in the axial direction of the drive shaft 17,thereby causing the pistons 28 to reciprocate through the shoes 29 inthe longitudinal direction of the compressor 10.

As shown in FIG. 1, a valve plate 31 is interposed between the rearhousing 14 and the cylinder block 12. The rear housing 14 definestherein at the center a suction chamber 32 and at the radially outerregion a discharge chamber 33, respectively. The suction chamber 32 andthe discharge chamber 33 are in communication with a compression chamber30 in each cylinder bore 12 a through a suction port 31 a and adischarge port 31 b formed in the valve plate 31, respectively.Meanwhile, as the piston 28 moves from its top dead center toward itsbottom dead center, refrigerant gas in the suction chamber 32 is drawninto the compression chamber 30 through the suction port 31 a. As thepiston 28 moves from its bottom dead center toward its top dead center,the refrigerant gas which has been drawn in the compression chamber 30is then compressed to a predetermined pressure and discharged into thedischarge chamber 33 through the discharge port 31 b.

The compressor 10 has a displacement control valve 34 which is disposedin the rear housing 14 for changing the inclination angle of the swashplate 22 thereby to adjust the stroke of the pistons 28 or thedisplacement of the compressor 10. The displacement control valve 34 isarranged in a supply passage (not shown) which connects the dischargechamber 33 to the crank chamber 16. The pressure in the crank chamber 16depends on the balance between the amount of high-pressure refrigerantgas introduced from the discharge chamber 33 into the crank chamber 16through the supply passage and the amount of refrigerant gas flowingfrom the crank chamber 16 into the suction chamber 32 through a bleedpassage (not shown) which connects the crank chamber 16 to the suctionchamber 32, which balance is adjusted by changing the opening of thedisplacement control valve 34. Thus, the pressure difference between thepressure in the crank chamber 16 and the pressure in the compressionchamber 30 through the piston 28 is varied thereby to change theinclination angle of the swash plate 22.

As shown in FIG. 2, the swash plate 22 has a round hole 22 b which isformed at a portion R of the outer periphery thereof where an imaginaryplane passing through the point of intersection O between the lineconnecting the top dead center position P and the bottom dead centerposition Q of the swash plate 22 and the axial line m of the drive shaft17 in perpendicular relation to the line between P and Q intersects withthe outer periphery of the swash plate 22. The round hole 22 b isrecessed from the outer peripheral surface 22 c of the swash plate 22toward the axial line m of the drive shaft 17. The magnet 35 or apermanent magnet is disposed in the round hole 22 b. The cylinder block12 has a plurality of through holes 12 c which are formed in theperipheral wall 12 b thereof between the piston 28 and the bolt 15 andarranged in parallel relation to the axial line m of the drive shaft 17at position where the through holes 12 may face the magnet 35 in theswash plate 22. A plurality of magnetic sensors 36 (five magneticsensors 36 a, 36 b, 36 c, 36 d and 36 e in this preferred embodiment)are disposed in the through holes 12 c, respectively. Hall elements areused as the magnetic sensors 36 for detecting the position of the swashplate 22.

Referring to FIGS. 3 and 4, the maximum and minimum inclination anglepositions of the swash plate 22 are indicated by the solid line and thechain double-dashed line, respectively. The swash plate 22 is inclinablebetween the minimum and the maximum inclination angles. As theinclination angle of the swash plate 22 is changed between the minimumand the maximum inclination angles, the outer peripheral portion R ofthe swash plate 22, in which the magnet 35 is disposed, is displacedparallel to the axial line m of the drive shaft 17. For the sake of thedescription, positions on the outer peripheral portion R of the swashplate 22 at its minimum and maximum inclination angles are defined asspot R0 and spot R1, respectively. A distance Δg of displacement of theouter peripheral portion R of the swash plate 22 from the spot R0 isdirectly proportional to the inclination angle of the swash plate 22.

As shown in FIG. 4, the distances between the spots R0 and R1 and theperipheral wall 12 b in the radial direction from the axial line m ofthe drive shaft 17 toward the peripheral wall 12 b, more specifically,the spaced distances between the spots R0 and R1 and the points ofintersection between lines passing through the spots R0 and R1 inperpendicular relation to the axial line m of the drive shaft 17 and theperipheral wall 12 b of the cylinder block 12 are referred to asdistances h and i, respectively. These distances h and i aresubstantially the same. In other words, the spaced distance between theouter peripheral portion R of the swash plate 22 and the peripheral wall12 b in the radial direction remains substantially constant when theinclination angle of the swash plate 22 is changed. Incidentally, thespaced distance between any other point on the periphery of the swashplate 22, e.g. the top dead center position P, and the peripheral wall12 b of the cylinder block 12 in the radial direction varies with theinclination of the swash plate 22 between the minimum and maximuminclination angles as indicated by symbols k and j in FIG. 3, whereinthe distance j is smaller than the distance k. Therefore, the distancebetween the magnet 35 provided in the outer peripheral portion R of theswash plate 22 and the peripheral wall 12 b in the radial directionremains substantially constant when the swash plate 22 is rotated whilechanging its inclination angle. The magnet 35 is rotated while beingdisplaced for the displacement distance Δg in the axial direction fromthe spot R0 of the outer peripheral portion R of the swash plate 22 atits minimum inclination angle.

For detecting the position of the magnet 35, the magnetic sensors 36 areprovided in the peripheral wall 12 b of the cylinder block 12. As shownin FIG. 4, the five magnetic sensors 36 a through 36 e having the samespecifications are provided in a line in the range between the minimumand maximum inclination angle positions of the swash plate 22. Themagnetic sensor 36 a is located at a position where it faces the magnet35 when the swash plate 22 is inclined at the minimum inclination angle.The magnetic sensor 36 e is located at a position where it faces themagnet 35 when the swash plate 22 is inclined at the maximum inclinationangle. The other magnetic sensors 36 b through 36 d are located atpositions corresponding to the positions of the magnet 35 atintermediate inclination angles of the swash plate 22.

The magnetic sensors 36 a through 36 e are operable to sense magneticflux density and send an electrical signal indicative of the sensed fluxdensity to a control unit (not shown) which is connected to the magneticsensor 36. The control unit determines the position of the magnet 35 andhence the current position of the swash plate 22 according to themagnitude of the magnetic flux density sensed by each magnetic sensor36. The control unit stores therein data about the displacement distanceΔg of the swash plate 22 corresponding to each of the magnetic sensors36 a through 36 e and also data of the relation between the displacementdistance Δg and the inclination angle of the swash plate 22. The controlunit is operable to perform arithmetic processing based on a certainprogram to calculate the inclination angle of the swash plate 22,thereby determining the displacement of the compressor 10.

The following will describe the operation of the compressor 10 of thispreferred embodiment. As the drive shaft 17 is rotated, the swash plate22 is rotated with a wobbling motion. Accordingly, the piston 28reciprocates in the cylinder bore 12, thus the compressor 10 performingsuction, compression and discharge of the refrigerant gas. Theinclination angle of the swash plate 22 is adjusted by the displacementcontrol valve 34 which controls the pressure difference between thepressure in the crank chamber 16 and the pressure in the compressionchamber 30 through the piston 28. When the magnet 35 is located, forexample, at spot R2 where the outer peripheral portion R of the swashplate 22 has been displaced for a displacement distance Δg2 from thespot R0 as shown in FIG. 4, the magnetic sensors 36 a through 36 e sensethe magnetic flux density at each location thereof and send thedetection signals to the control unit.

In this case, the magnet 35 is located closest to the magnetic sensor 36c in facing relation thereto. Thus, the magnetic flux density sensed bythe magnetic sensor 36 c is the greatest and, therefore, the controlunit determines that the swash plate 22 is located at the spot R2corresponding to the position of the magnetic sensor 36 c. Furthermore,the control unit performs the arithmetic processing based on the programaccording to the detection signal thereby to calculate the inclinationangle of the swash plate 22.

The following advantageous effects are obtained according to the firstpreferred embodiment.

(1) The magnet 35 is provided in the portion R of the outer periphery ofthe swash plate 22 where the imaginary plane passing through the pointof intersection O between the line connecting the top dead centerposition P and the pottom dead center position Q of the swash plate 22and the axial line m of the drive shaft 17 in perpendicular relation tothe line between P and Q intersects with the outer periphery of theswash plate 22. By virtue of such arrangement, the magnet 35 isdisplaced only in axial direction by the change of inclination angle ofthe swash plate 22. In other words, the distance between the magneticsensor 36 provided in the peripheral wall 12 b and the magnet 35 isvariable in the axial direction but remains constant in the radialdirection. Therefore, the displacement of the magnet 35 in the axialdirection is accurately detected by the magnetic sensor 36, with theresult that the inclination angle of the swash plate 22, which isproportional to the displacement of the magnet 35, is accuratelydetected.

(2) The minimum inclination angle position of the swash plate 22 is setas the base point for detection of the magnet 35 which is provided inthe swash plate 22 and displaceable in the axial direction from the basepoint. Thus, the displacement distance Δg of the magnet 35 from the basepoint corresponding to the inclination angle of the swash plate 22 isdetected by the magnetic sensor 36, thereby accurately detecting theinclination angle of the swash plate 22.

(3) The five magnetic sensors 36 a through 36 e are aligned in the axialdirection in the range between the minimum and maximum inclination anglepositions of the swash plate 22 and located at positions eachcorresponding a predetermined displacement distance Δg as measured fromthe base point. When the magnet 35 is displaced in the axial directionwhile the inclination angle of the swash plate 22 is changed, any one ofthe magnetic sensors 36 a through 36 e which is then positioned closestto the magnet 35 detects the magnet 35. Thus, the inclination angle ofthe swash plate 22 is detected with an increased accuracy.

(4) The distance between the magnet 35 in the swash plate 22 and therespective magnetic sensors 36 in the radial direction is substantiallyconstant. Therefore, there is no need to make distance correction of themagnetic sensors 36 a through 36 e due to change of the above distancein the radial direction in making the detection sensitivity adjustmentof the magnetic sensors 36 a through 36 e. Thus, the setting-upadjustment of the magnetic sensors 36 is simplified.

(5) The magnet 35 and the magnetic sensor 36 are easy to handle and theyare merely fixed in the swash plate 22 and the peripheral wall 12 b,respectively, thus easy to assemble.

(6) The magnetic sensor 36 is provided in the peripheral wall 12 b ofthe cylinder block 12 between the piston 28 and the bolt 15 and,therefore, there is no intermediate between the magnetic sensor 36 andthe magnet 35. Thus, magnetic flux density of the magnet 35 provided inthe swash plate 22 is accurately detected by the magnetic sensor 36.

The following will describe a variable displacement compressor accordingto a second preferred embodiment of the present invention with referenceto FIGS. 5 and 6. The second preferred embodiment differs from the firstpreferred embodiment in that only one magnetic sensor is provided in thecompressor 10. The other structure of this compressor is substantiallythe same as that of the first preferred embodiment. For convenience ofexplanation, common or similar elements or parts are designated by thesame reference numerals as those of the first preferred embodiment and,therefore, the description thereof is omitted and only the modificationswill be described.

Referring to FIG. 6, a magnetic sensor 40 is provided in the peripheralwall 12 b of the cylinder block 12 at a position where the magneticsensor 40 faces to the magnet 35 when the swash plate 22 is inclined atthe minimum inclination angle. The magnetic sensor 40 detects magneticflux density of the magnet 35 and send an electrical signalrepresentative of the sensed flux density to the control unit. Themagnetic sensor 40 detects the position of the swash plate 22 (or thedisplacement distance Δg in the axial direction from the base point)according to magnitude of the sensed magnetic flux density. The controlunit stores therein data of the relation between the detection output(or the magnitude of magnetic flux density) of the magnetic sensor 40and the displacement distance Δg of the swash plate 22 and also data ofthe relation between the displacement distance Δg and the inclinationangle of the swash plate 22. The control unit performs arithmeticprocessing based on a certain program to calculate the displacementdistance Δg of the swash plate 22 and the inclination angle of the swashplate 22, thus obtaining information concerning the displacement of thecompressor 10.

According to the compressor of the second preferred embodiment, the sameadvantageous effects as mentioned in the paragraphs (1), (2), (5) and(6) for the first preferred embodiment are obtained. The secondembodiment offers additional advantages as follows.

The magnetic sensor 40 is provided so as to face the magnet 35 when theswash plate 22 is positioned at the minimum inclination angle. Thus, asthe magnet 35 is displaced in the axial direction with the inclinationof the swash plate 22, the magnetic flux density of the displaced magnet35 is detected by one magnetic sensor 40 for calculation by the controlunit of the displacement distance Δg from the base point of the swashplate 22 and the inclination angle of the swash plate 22. As a result,the number of parts is reduced and the device is made simpler instructure.

The present invention is not limited to the embodiments described abovebut may be modified into various alternative embodiments as exemplifiedbelow.

In the first and second preferred embodiments, the magnet 35 is providedin the outer peripheral portion R of the swash plate 22 where theimaginary plane passing through the point of intersection O between theline connecting the top dead center position P and the bottom deadcenter position Q of the swash plate 22 and the axial line m of thedrive shaft 17 in perpendicular relation to the line between P and Qintersects with the outer periphery of the swash plate22. Alternatively,the magnet may be provided at a portion S of the outer periphery of theswash plate 22 that is opposite to the outer peripheral portion R, asshown in FIG. 2. The magnetic sensor may be provided in facing relationto the magnet. As a further alternative of the invention, in addition tothe magnet 35 at the outer peripheral portion R of the swash plate 22,another magnet 37 may be provided at the outer peripheral portion S ofthe swash plate 22 as shown in FIG. 7. In this case, reliability ofdetection is enhanced.

The object to be detected and the detector are provided by the magnetand the magnetic sensor in the first and second preferred embodiments.Alternatively, any magnetic material may be used as the detection objectinstead of the magnet. Any other types of magnetic sensors such asmagneto-inductive sensor, magneto-resistive (MR) sensor,magneto-impedance (MI) sensor and the like other than the Hall elementmay be used.

The detection object and the detector are not limited to the magnet andthe magnetic sensor, respectively. Alternatively, they may be of varioustypes such as ultrasound type, optical type and the like.

The magnetic sensor 36 is provided in the peripheral wall 12 a of thecylinder block 12 in the first and second preferred embodiments.Alternatively, a magnetic sensor 41 may be connected to the bolt 15which is provided adjacent to the peripheral wall 12 a of the cylinderblock 12 for joining the housing members (the front housing 13, thecylinder block 12 and the rear housing 14) as shown in FIG. 8. Or, anyother fitting member may be provided and the magnetic sensor may befixed thereto. Fox example, a fitting member 42 may be provided to thecylinder block 12 and a magnetic sensor 43 may be fixed to the fittingmember 42 as shown in FIG. 9.

Therefore, the present examples and embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein but may be modified within the scope of theappended claims.

1. A displacement detection device for a variable displacementcompressor in which a swash plate is connected to a piston through shoesin a housing, the swash plate slides relative to the shoes and rotatessynchronously with a drive shaft with a wobbling motion in an axialdirection of the drive shaft as the drive shaft is rotated, and aninclination angle of the swash plate is controlled thereby to change astroke of the piston, comprising: a detection object provided in a firstportion of an outer periphery of the swash plate where an imaginaryplane passing through a point of intersection between a line connectinga top dead center position and a bottom dead center position of theswash plate and an axial line of the drive shaft in perpendicularrelation to the line intersects with the outer periphery of the swashplate; and a detector provided in the housing so as to face thedetection object.
 2. The displacement detection device according toclaim 1, wherein the detector is located in a range between a minimuminclination angle position of the swash plate and a maximum inclinationangle position of the swash plate.
 3. The displacement detection deviceaccording to claim 1, wherein the detection object is a magnet or amagnetic material.
 4. The displacement detection device according toclaim 3, wherein the detector is a plurality of the magnetic sensorswhich are provided in a peripheral wall of the housing and alignedparallel to the axial line of the drive shaft.
 5. The displacementdetection device according to claim 3, wherein the detector is amagnetic sensor.
 6. The displacement detection device according to claim5, wherein the magnetic sensor is a Hall element, a magneto-inductivesensor, a magneto-resistive sensor or a magneto-impedance sensor.
 7. Thedisplacement detection device according to claim 1, wherein thedetection object and the detector are of ultrasound type or opticaltype.
 8. The displacement detection device according to claim 1, furthercomprising another detection object provided in a second portion of theouter periphery of the swash plate opposite to the first portion.
 9. Thedisplacement detection device according to claim 1, wherein the housingincludes a plurality of housing members which are joined to each otherby a bolt, the detector being connected to the bolt.
 10. Thedisplacement detection device according to claim 1, further including afitting member which is provided to the housing, the detector beingfixed to the fitting member.